More than four-and-a half thousand people have applied to take part in a joint Russian-European venture in which six people will be locked inside a mock spacecraft for 520 days to simulate an expedition to Mars.

Russia's space agency is sifting through piles of applications from would-be astronauts, including Britons, prepared to suffer extreme privation to test endurance levels for a Mars odyssey.

Successful candidates will be locked inside a cramped barrel-shaped spacecraft in central Moscow for a year and a half: 250 days to Mars, followed by a month on the surface, and 240 days to get back. The craft comprises tiny modules - a claustrophobic 550 cubic metres in total that aims to replicate the psychological pressures of an arduous long-distance space voyage.

Mark Belakovsky, head of the Mars 500 project, said yesterday: "We want applicants who are healthy and professional. They have to be intellectually tough."

Dr Belakovsky, of the Institute of Biomedical Problems, said male and female applicants had to be aged 25 to 50. Doctors would be preferred, he said.

"We've had applicants from Britain," he added. "If British firms would like to supply us with books, films, or food we would be happy to hear from them."

The institute and the European Space Agency (ESA) are separately considering applications for the mock voyage as well as two experiments in November and early 2008, also with crews of six.

ESA will select two of the six crew members. "So far, 4,600 people have applied. Most say that they've been interested in space flight since childhood but for personal reasons haven't got round to it," an ESA spokeswoman said.

Once the main study gets under way crew members will remain on board for the duration, barring emergencies. "They will have taken off, and that's it," Dr Belakovsky said.

Astronauts will be exposed to all aspects of life in space, apart from radiation and weightlessness. Communicating with mission control will be subject to a 20-minute delay: the time taken to send a signal to Earth. Before they "land", three astronauts destined to "live" on Mars will spend a month in a separate module, lying on their backs with their heads lower than their feet to simulate zero gravity.

The crew will spend most of their time in a 150 cubic metre living module, which has personal cabins, as well as a common room and kitchen. Volunteers will be paid for taking part in the study.

All food and water will be taken on board before the trip. Alcohol and smoking will be forbidden, and sex frowned upon. "It's not a reality show - it is a serious pioneering research experiment," Dr Belakovsky told Associated Press, adding that there would be moments of tension.

"If you and your girlfriend were to shut yourselves in a room for three days, five days, a month - believe me, you would have a million problems. Either she would strangle you or you would strangle her. Anything can happen," he said.

Dr Belakovsky conceded that a real manned mission to Mars was unlikely to get under way before the late 2020s. In 2004 President George Bush described landing on Mars as a long-term goal of Nasa. The European Space Agency hopes to get humans there by 2035.

In the meantime experts are unsure whether Mars, which has polar ice caps that make it the most Earth-like planet in the solar system, might harbour life. Several probes have failed to find proof.